1. Field of the Invention
The present invention relates generally to sealing devices for pipe junctions, and more particularly, relates to a novel annular resilient gasket in combination with a non-resilient locking ring for use in forming a fluid-tight seal between the telescoping ends of interconnected members of a bell and spigot type joint.
2. Discussion of the Prior Art
It is known to employ plastic pipes and fittings in the design and construction of underground conduit systems for conveyance of water under pressure and drainage purposes. Individual sections of plastic pipe are joined together in end to end juxtaposition and suitable fittings are employed intermediate the pipe sections to construct changes in direction, branch connections and the like. A most common method employed in joining the pipe sections and fittings is the so-called bell and spigot joint wherein one end of a pipe or fitting is enlarged or "belled" to receive therein the unenlarged or "spigot" end of the adjacent length of pipe. The inside diameter of the belled section or hub is formed sufficiently large to receive therein the spigot end of the next adjacent section of pipe with sufficient annular clearance to provide for the application of packing, caulking, gaskets or other devices which are designed to prevent leakage at the pipe joints when the pipe sections and fittings are joined into a pipe line. Depending upon the intended pressure at which the fluid will be conveyed within the pipe system, other design parameters such as the wall thickness of the pipe and the type of material of the pipe, the type of seal between adjacent lengths of pipe, the configuration of the bell, etc., will require more or less sophisticated design considerations.
Particularly in the plastic pipe industry, it is the common practice to provide a rubber or other elastomeric material gasket to form the seal between adjacent pipe sections or at the junction between a pipe and a fitting. Such gaskets have been configured and designed to facilitate the making up of the pipe joint in the shortest possible period of time in a manner to prevent leakage at the joint upon completion of the system. As the design operating pressures in a piping system increase, the difficulties encountered in providing an efficient and reliable seal have also increased.
In efforts to solve the sealing problems at pipe joints which are inherent in pressure or vacuum piping systems, prior workers in the art have developed gaskets of the type including one or more radially inwardly extending lips to press against the spigot end of the connected section of pipe. Additionally, other workers have provided gaskets having an internal peripheral groove within which is seated a locking ring of relatively hard plastic material to prevent movement of the seal as the joint is made up and to discourage gasket blow out when surges in system pressure occurred. In other efforts to prevent unseating of the gasket when the pipe joint was made up or to aid in preventing gasket blow out under severe pressure conditions of use, prior workers have also developed means to lock the gasket within an annular groove which could be formed in the plastic material of the bell during the belling operation.
In U.S. Pat. No. 4,343,480, entitled "Pipe Bell and Gasket", which patent is owned by the assignee of the present application, there is disclosed a bell and spigot connection for plastic pipes which employs a gasket groove in the hub and a gasket having a pair of longitudinally spaced, radially inwardly extending lips which is seated within the gasket groove. The gasket may be employed either with or without a hard plastic retaining ring intermediate the lips. In the patented configuration, the exterior or entrance end of the hub was radially inwardly bent after the gasket was seated in the hub groove to retain the gasket within the gasket receiving groove in a manner to prevent gasket blow out upon surges in system pressure.
Other patents wherein gaskets with radially inwardly projecting lips are disclosed, among others, are U.S. Pat. Nos. 2,980,443, 3,081,102 and 4,379,559.
All of the prior art gaskets of which we are aware were formed of relatively thick sections of rubber or other elastomeric material and this thickness was required to prevent tearing of the gasket upon making up of the joint and to discourage gasket blow out at operating pressures. Due to the thickness of the gasket material that has been required to produce a satisfactory product, the presently available gasket sealing means tend to be quite expensive in manufacture and therefore significantly increase the overall costs of the pipes and fittings which comprise a piping system.